(1) Field of the Invention
This invention relates to a process for reacting phenol, mono- and di-alkyl phenols having at least one free o-position with methanol and/or dimethyl ether in the gas phase to form o-substituted phenols in the presence of a catalyst of oxides of iron, chromium, silicon and at least one oxide of an alkaline-earth metal, lanthanum and manganese or in the presence of a catalyst of oxides of iron, chromium, a metal from the group comprising germanium, titanium, zirconium, tin, lead, and at least one oxide of an alkali metal, alkaline-earth metal, lanthanum and manganese.
(2) Description of the Prior Art
The production of o-substituted phenols, for example 2,6-dimethyl phenol or 2,3,6-trimethyl phenol, is of considerable commercial interest because of the first of these two phenol derivatives is required for numerous applications, particularly the production of polyphenylene oxide, whilst the second derivative may be used for example as a preliminary stage in the production of vitamin E. Although synthesis processes are known from the patent literature, there has never been a process by which o-substitution products can be obtained highly selectively from phenols having free o-positions with production times that are long enough for practical application. Although phenol can be reacted to form 2,6-dimethyl phenol with a selectivity of the order of 99% in accordance with German Offenlegungsschrift No. 21 27 083, a selectivity of only 95% is obtained where o-cresol is used as the starting material.
German Offenlegungsschrift No. 19 48 607 describes a process in which o-cresol is converted into 2,6-dimethyl phenol with a selectivity of around 84%. Conversely, a selectivity of 98% is obtained with o-cresol as the starting product according to German Offenlegungsschrift No. 24 28 056. Where phenol is used, however, a selectivity of only 96,5% is achieved, falling to 92% after 150 hours. According to German Offenlegungsschrift No. 25 47 309, 2,4,6-trimethyl phenol is obtained in a yield of 95% by methylating p-cresol, 2,3,6-trimethyl phenol being obtained in a yield of 94% from m-cresol, whereas according to German Offenlegungsschrift No. 23 29 812, 2,3,6-trimethyl phenol is obtained in a yield of 82% from m-cresol.